1. Field of the Invention
The present invention relates to novel sialic acid-bonded octapeptides and a method for preparing these octapeptides and more particularly to derivatives of an octapeptide similar to a serum thymic factor, FTS (Facteur Thymique Serique), effective as a drug for treating the lowering and abnormality of functions of the thymus and a method for preparing the same.
2. Description of the Prior Art
FTS which is a thymic factor is a peptide comprising 9 amino acid molecules and it has been isolated from blood by J. Bach et al. in 1976. This factor is produced in the thymus and is a physiologically active substance having an effect of inducing mature T cells by exerting an influence on T cells which pass through the thymus to promote proliferation and differentiation. This factor would be used as a medicine for treating the lowering and abnormality of functions of the thymus or the like. Thus, it has already been organochemically synthesized and its basic and clinical applications have been investigated.
However, the half life of FTS in blood is very short value of the order of several tens minutes and, therefore, a sufficient sustained effect thereof is not expected when it is administered to an organism or living body.
Under such circumstances, there has been a requirement for the development of novel compounds having physiological activity comparable to FTS and a longer half life in blood.